This project is concerned with development of in vitro assays for detection, enumeration, and characterization of cells which synthesize one or more components of the complement system. Of particular concern are cells synthesizing C4 and/or C3. Conditions which regulate synthesis are to be explored. Patterns of cell surface distribution of these components will be determined by ultrastructural enzyme immunohistochemical and immunoferritin techniques. Relationship of cell surface complement components on macrophages, the principle cells of origin of at least C4 and C3, to function of these cells in antigen capture and processing, immune responses, and target cell cytotoxicity will be determined.